Conventionally, logs have been graded primarily by visual inspection of the logs by an inspector who assigns a grade to the log based upon how the log appears to him. This log grading is highly subjective depending on the skill of the inspector and is prone to error. The present invention provides an automatic log grading technique using ultrasonic testing which detects internal defects within the log that cannot be seen visually and is therefore more accurate that visual inspection log grading.
Previously, the distance to a log has been determined by using ultrasonic waves to measure the diameter of the log at several longitudinal positions along the log in order to determine the optimum yield axis of the log for a veneer lathe or sawmill. In this regard see U.S. Pat. No. 4,356,850 of Halgrimson, et al., issued Nov. 2, 1982, and U.S. Pat. No. 4,412,297 of Halgrimson, et al., issued Oct. 25, 1983. However, in these prior methods sound waves are transmitted through the air and reflected off the surface of the log to the ultrasonic transducer from which they were emitted and sound waves are not transmitted through the log to determine internal defects in the manner of the present invention.
Previously it has been proposed to provide mechanical sensor means in the form of wheels which engage the log to determine the length and diameter of the log for automatic grading purposes using a computer as shown in U.S. Pat. 3,554,249 of Vasteras, et al., issued Jan. 12, 1971. However, unlike the present invention, this grading apparatus does not employ ultrasonic testing for detecting internal defects within the log and grading the log based upon such tests.
It has also been proposed to grade lumber by visual observation of a grader who looks at the surface of the lumber, as disclosed in U.S. Pat. No. 4,023,605 of Hellstrom, et al., issued May 17, 1977, and U.S. Pat. No. 3,759,384 of Holmberg, et al., issued Sept. 18, 1973. In addition, lumber has been inspected automatically by light scanning to determine surface defects as shown in U.S. Pat. No. 4,207,472 of Idelsohn, et al., issued June 10, 1980, and U.S. Pat. No. 4,149,089 of Idelsohn, et al., issued Apr/ 10, 1979. However, none of these patents disclose the use of ultrasonic sound waves transmitted through the interior of the log to detect internal defects in order to provide more accurate grading of the log in the manner of the present invention.
It has previously been proposed in U.S. Pat. No. 4,169,173 of Bergholm, et al., issued Sept. 25, 1979, to color mark logs to indicated their length, by automatically controlled paint sprayers. However, this patent does not deal with ultrasonic grading of logs and color marking them in accordance with the grade so determined, in the manner of the present invention.
In the unrelated field of the grading of meat, such as hog carcasses, such grading has been done by using ultrasonic testing to determine the fat thickness, as shown in U.S. Pat. No. 4,785,817 of Stouffer, issued Nov. 22, 1988, U.S. Pat. No. 3,722,263 of Hautaniemi, et al., issued Mar. 27, 1973 and U.S. Pat. No. 4,099,420 of Stouffer, et al., issued July 11, 1978. In this latter patent a fluid couplant is employed to couple the transducer to the surface of the body of the animal carcass. However, unlike the ultrasonic log grader apparatus of the present invention, this patent employs a closed chamber for the fluid couplant and slides the transducer and such chamber along the surface of the animal carcass, which is only possible because of the soft, smooth surface of such carcass
Also of interest is U.S. Pat. No. 4,027,528 of Tyree, issued June 7, 1977, which shows liquid coupling for an ultrasonic transducer used in inspecting metal wall members such as steel tanks, ship hulls, and the like.
Previously it has also been proposed, in a research laboratory, to detect defects in lumber by submerging the lumber in a water tank and transmitting ultrasonic waves through the water into the lumber. This is not commercially practical for grading logs in the field immediately after the logs are cut.